Various work machines such as tractors, skid steer loaders, forest machines, excavators and a wide variety of other work machines typically have a large number of hydraulically controlled work tools or attachments that are attachable or mountable to the particular work machine to perform a particular work function. A work tool can be a work enabling implement such a bucket, blade, ripper, drill, and a grapple. These work tools or attachments are typically controlled through a control system which typically includes one or more hydraulic systems which are used to actuate and control the work tool lift, extend/retract, and/or tilt mechanisms.
Work machines with work tools systems actuated with hydraulic systems include an actuating hydraulic cylinder assemblies to actuate and control the work tools. Further, the hydraulic systems include hydraulic control valves to allow control flow of hydraulic fluid and regulate hydraulic pressure within the hydraulic systems when work implements are subject to over-running loads. For example, in a forestry machine such as a log grapple, hydraulic check valves allow to hold load on the grapple tongs.
In the forestry machine, although the check valve may allow to hold load, however during certain work conditions, the grapple tong cylinder head-end may experience very high pressures (in the 10 kPSI range) which can cause damage to the hydraulic circuits. One such example can be during ‘drop-and-catch’ operations (wood logs are being repositioned inside the tongs by being dropped and caught again in mid-air) of the grapple tongs, the grapple tong actuation cylinder head-end experiences very high pressures.
U.S. Pat. No. 5,558,380 filed by Douglas and Stanley discloses a hydraulic system for a grapple. The hydraulic system includes a cross over relief valve assembly comprising two pressure relief valves connected in parallel with the flow divider valve. However, the '380 patent does not disclose any solution during momentarily high pressure experienced in the grapple tong actuation cylinder during the ‘drop-and-catch’ operations of the grapple.
The presently disclosed system is directed to overcoming one or more of the problems set forth above.